Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica
<p>The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase functi...
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Copernicus Publications
2020-11-01
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| Series: | The Cryosphere |
| Online Access: | https://tc.copernicus.org/articles/14/3959/2020/tc-14-3959-2020.pdf |
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| author | T. Carlsen T. Carlsen G. Birnbaum A. Ehrlich V. Helm E. Jäkel M. Schäfer M. Wendisch |
| author_facet | T. Carlsen T. Carlsen G. Birnbaum A. Ehrlich V. Helm E. Jäkel M. Schäfer M. Wendisch |
| author_sort | T. Carlsen |
| collection | DOAJ |
| description | <p>The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above
snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of
the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and
Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived
from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180<span class="inline-formula"><sup>∘</sup></span> fish-eye camera (green channel,
490–585 <span class="inline-formula">nm</span> wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain
sizes, and solar zenith angles. The airborne observations covered an area of around 1000 <span class="inline-formula">km</span> <span class="inline-formula">×</span> 1000 <span class="inline-formula">km</span> in the vicinity of
Kohnen Station (75<span class="inline-formula"><sup>∘</sup></span>0<span class="inline-formula"><sup>′</sup></span> S, 0<span class="inline-formula"><sup>∘</sup></span>4<span class="inline-formula"><sup>′</sup></span> E) at the outer part of the East Antarctic Plateau. The observations include
regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward,
angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces
(sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional
reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface
roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate
Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 <span class="inline-formula">nm</span> wavelength
band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight
<span class="inline-formula"><i>f</i><sub>vol</sub></span> (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties.</p> |
| first_indexed | 2024-12-11T04:24:32Z |
| format | Article |
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| issn | 1994-0416 1994-0424 |
| language | English |
| last_indexed | 2024-12-11T04:24:32Z |
| publishDate | 2020-11-01 |
| publisher | Copernicus Publications |
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| series | The Cryosphere |
| spelling | doaj.art-7004077e7fd9425f922070321ebb82ec2022-12-22T01:21:00ZengCopernicus PublicationsThe Cryosphere1994-04161994-04242020-11-01143959397810.5194/tc-14-3959-2020Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in AntarcticaT. Carlsen0T. Carlsen1G. Birnbaum2A. Ehrlich3V. Helm4E. Jäkel5M. Schäfer6M. Wendisch7Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germanynow at: Department of Geosciences, University of Oslo, Oslo, NorwayAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany<p>The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180<span class="inline-formula"><sup>∘</sup></span> fish-eye camera (green channel, 490–585 <span class="inline-formula">nm</span> wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain sizes, and solar zenith angles. The airborne observations covered an area of around 1000 <span class="inline-formula">km</span> <span class="inline-formula">×</span> 1000 <span class="inline-formula">km</span> in the vicinity of Kohnen Station (75<span class="inline-formula"><sup>∘</sup></span>0<span class="inline-formula"><sup>′</sup></span> S, 0<span class="inline-formula"><sup>∘</sup></span>4<span class="inline-formula"><sup>′</sup></span> E) at the outer part of the East Antarctic Plateau. The observations include regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward, angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces (sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 <span class="inline-formula">nm</span> wavelength band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight <span class="inline-formula"><i>f</i><sub>vol</sub></span> (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties.</p>https://tc.copernicus.org/articles/14/3959/2020/tc-14-3959-2020.pdf |
| spellingShingle | T. Carlsen T. Carlsen G. Birnbaum A. Ehrlich V. Helm E. Jäkel M. Schäfer M. Wendisch Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica The Cryosphere |
| title | Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica |
| title_full | Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica |
| title_fullStr | Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica |
| title_full_unstemmed | Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica |
| title_short | Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica |
| title_sort | parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in antarctica |
| url | https://tc.copernicus.org/articles/14/3959/2020/tc-14-3959-2020.pdf |
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